The bloody hand has reached out to Lebanon once more, striking down one of its most prominent journalists and one of the most vociferous and bravest critics of the Syrian regime.

Samir Kassir was the best known columnist on An Nahar, a valued member of the opposition, newly married and - like so many of us in Beirut - living on the happy assumption that with Syria’s troops and intelligence officers withdrawn from Lebanon, he had nothing to fear.

So who murdered Samir Kassir?

"He always left home at 10.30am and I saw him walking across the street," a female neighbour told me yesterday. "He always left home at the same time. He opened the door of his car, sat inside and started the engine. Then the car blew up."

Close inspection of Mr Kassir’s Alfa-Romeo, registration number 165670, showed clearly the blast came from beneath the driver’s seat. It tore open the roof, blasted out the driver’s door, smashed the steering column and hurled Mr Kassir on to the passenger seat. The ignition seems to have detonated the bomb.

This was a shock that no one in Beirut expected - except, of course, the assassins. Germany’s top detective, Detlev Mehlis, is already here with his team to investigate the murder of the former prime minister Rafik Hariri in February. We all thought that Lebanon’s assassins were in their rabbit holes, fearful of arrest.

But no, they are still on operational duty, still in killing mode. Nassib Lahoud, the opposition MP and friend of Kassir - he may be the next Lebanese president - was in tears when I spoke to him beside Mr Kassir’s wrecked car. He talked about "criminal hands", about the "intelligence apparatus" who he blamed for the assassination. The only word he didn’t use was "Syria".

So who murdered Samir Kassir?

Just before he resigned this year, the pro-Syrian head of Lebanon’s General Security Service, Jamil Sayed, hysterically offered to arrest himself if he was blamed for Hariri’s murder. Mr Kassir had written a brutal article the next day, pointing out that it was good to see those who had threatened journalists and who had censored journalists now showing their own fear of justice. Rustum Ghazaleh, who was head of Syrian military intelligence in Lebanon, screamed abuse at the journalist.

So who murdered Samir Kassir?

In 2001, after a series of articles excoriating the Syrians and pro-Syrian Lebanese intelligence operatives, airport security confiscated his passport on his return from Amman, claiming they wanted to "verify the conditions upon which it was obtained".

Mr Kassir was of Palestinian origin but had travelled on his legally-issued Lebanese passport on 14 recent occasions. In 2001, he complained he was under surveillance and his neighbours claimed they were interrogated by intelligence officers.

So who murdered Samir Kassir?

Nassib Lahoud, who was last night attending a meeting of opposition leaders in Beirut - among them was the Druze leader, Walid Jumblatt, who was a close friend of Mr Kassir - had no doubts about the reasons for the murder. "Criminal hands did not target Samir because he was a brilliant journalist," he said. "They did not target Samir because he was a brilliant intellectual. They have targeted Samir for being one of the leaders of Lebanon’s spring, because he was part and parcel of the opposition. So the battle with the intelligence apparatus is not over. This assassination is meant to tell us that Lebanon’s march towards democracy should not be an easy ride."

Mr Kassir, who had two children from a previous marriage, had only recently married Giselle Khoury, a journalist on the Arabiya satellite channel. "Why don’t they leave us alone now?" one of their young neighbours asked me yesterday. "Why must they go on using this methodology of murder? We have to stop this. Are they trying to drive all the young people out of Lebanon?"

This week, An Nahar picked up a story that had been running in its rival paper, Mr Hariri’s daily Al-Mustaqbal, and named three prominent Syrian intelligence officers who it claimed had - in defiance of UN Security Council resolution 1559 - returned to Lebanon to interfere in elections.

Identifying Syria’s spooks is not a healthy thing to do. Their names were given as: Brigadier General Mohamed Khallouf - who was the senior Syrian intelligence officer in Beirut until last April - Nabil Hishmeh and Khalil Zogheib, who used to run Syria’s secret services in Tripoli. Syria denied the men were here. Mr Kassir’s last column - on Friday last week - was an attack on the Syrian Baath party, headlined "Mistake after mistake".